Wishbone-shaped booms are used in many applications of sailing and wind surfing. Traditionally the booms are made from curved wood or tubular aluminum elements which are bent and then joined with fittings at both the leading and trailing edges of the sail mast.
Such traditional curved booms, however, have several problems. For example, aluminum is subject to corrosion and fatigue failures, and it is further weakened by the joining of the tubes at the most heavily-loaded leading edge, where the boom attaches via the fittings to the sail mast.
Improved designs over the wood and aluminum booms utilize curved composite tubes, made from glass and carbon fiber with reinforced thermoset resins, which are fastened to an aluminum or plastic fitting at the boom front. Although this design is an improvement over a boom made with aluminum tubing, booms made from curved composite tubes are still particularly subject to failure at the heavily-loaded front end where there is a joint between the front end fitting and the composite tubes.
Thus, further improvements are desired in the performance and construction of wishbone-shaped booms, and in curved composite members generally. Accordingly, an object of this invention is to provide a composite tubular member of high stiffness which can be formed into a continuous selectively-shaped tube thereby eliminating the joints necessary affix the mast to the boom.
A further object of this invention is to provide a composite tubular member which has variable bending stiffness along it's length to maximize the overall resistance of the wishbone boom to bending loads which result from wind forces on the sail.
Yet another object of the invention is to provide a composite structural member which may be formed into a predetermined shape, e.g., a sailboard boom, via a secondary processing of heating and bending.
These and other objects of the invention will become apparent in the description which follows.